Electromagnetic valve actuators are known that comprise electromagnetic means for moving a moving member comprising an armature secured to a rod connected to the stem of the valve, which moving member is moved between a position in which the valve is closed and a position in which the valve is open. The electromagnetic means are controlled via a servo-control system operating in particular as a function of the position of the moving member and taking the speed of the moving member into account. The speed of the moving member is obtained by digitally differentiating its position as supplied by a position sensor such as a Hall effect sensor. Sensors of that type operate by means of permanent magnets secured to the stem. Nevertheless, it is very difficult to put such magnets into place. The complexity of the sensors also limits their reliability. In addition, such position sensors include active elements that need to be electrically powered in order to operate.